Field of Invention
The present invention relates to a micro-electron-mechanical system (MEMS) device; particularly, it relates to such MEMS device having its stopper anchored to a proof mass frame which is apart of a proof mass. Therefore, while the stopper provides the function to constraint the displacement of a main body of the proof mass, the stopper also contributes to increase the mass quantity of the proof mass so as to increase the sensitivity of the MEMS device.
Description of Related Art
MEMS devices, for example inertial sensors, accelerometers, gyroscopes, etc., include a suspended structure which is movable relatively to a fixed structure. The suspended structure includes a proof mass and the proof mass includes a movable electrode. The fixed structure includes a fixed electrode. The relative movement between the suspended structure and the fixed structure causes a capacitance change between the movable electrode and the fixed electrode. This capacitance change can be read out as a sensing signal indicating the movement.
It is preferred that the suspended structure does not move beyond a certain range. However, due to an external event, for example an impact or shock, the suspended structure can make a sudden undesired movement which may cause a damage of the MEMS device. For this reason, stopper structures (generally known as “stoppers”) are provided in the MEMS device.
Conventionally, stoppers are provided as apart of the fixed structure, which is fixed to a substrate of the MEMS device. U.S. Pat. No. 5,542,295, U.S. Pat. No. 6,360,605 and U.S. Pat. No. 7,000,473 are examples of such stoppers. However, such conventional design of stoppers consumes space but does not increase the sensitivity of the MEMS device.
In view of the above drawback in the prior art, the present invention proposes a MEMS device having its stopper anchored to a proof mass frame which is apart of a proof mass. Therefore, while the stopper provides the function to constraint the displacement of a main body of the proof mass, the stopper also contributes to increase the mass quantity of the proof mass so as to increase the sensitivity of the MEMS device.